Revealing mistake: The knife that Leela kills Meeker with is very obviously loosely attached to his clothes. It wobbles back and forth after he falls.
Revealing mistake: In episode 3, the section of wall K-9 knocks down is obviously precut, complete with debris on the floor.
Revealing mistake: When K-9 shoots one of the infected men, the blast beam appears to come out of his eyes, then moves down to his snout as the camera moves.
Answer: TARDISes are generally available for properly authorised use on Gallifrey; they're not usually assigned to a particular Timelord on a long-term basis. The Doctor stole his when he left his homeworld.
Tailkinker ★